TM 1-1500-204-23-9Figure 3-39. Using Outside MicrometerFigure 3-40. Using Inside Micrometer withExtension Rodbe sure the tool is spanning the true diameter of a holeor the correct width of a slot.(b) Handle attachment. For probing a deephole or a restricted place, a handle attachment may beused. The handle clamps on to the body of themicrometer.d. ReadingaStandardMicrometer. Reading amicrometer is a matter of reading the micrometer scaleor counting the revolutions of the thimble, and adding tothis any fraction of a revolution (see figure 3-41).(1) Spindle movement. The micrometer screwhas 40 threads per inch. This means that one completeand exact revolution of the thimble (3) moves thespindle (2) toward or away from the anvil (1) exactly1/40 or 0.025 inch.(2) Barrel measurements. The followingparagraphs describe the markings which are inscribedon the micrometer barrel and thimble (see figure 3-42).(a) Barrel lines. The lines on the barrel (1)conform to the pitch of the micrometer screw under theFigure 3-41. Parts of a Micrometer3-16